Author: glebius
Date: Mon Apr 4 07:45:08 2011
New Revision: 220317
URL: http://svn.freebsd.org/changeset/base/220317
Log:
When removing ifnets, we should first remove the reference to ifnet
from the interface index, then decrease refcount, not vice versa.
Otherwise there is a race (reproducible) when if_free_internal()
contests on IFNET_WLOCK(), and we got a zero-refed ifnet in the
index for a long time. It may be picked by some other thread,
that runs ifnet_byindex_ref(), who takes the ifnet from index,
and bumps refcount. When reader drops the lock, if_free_internal()
proceeds with free. Then reader tries to free it a second time.
Modified:
head/sys/net/if.c
Modified: head/sys/net/if.c
==============================================================================
--- head/sys/net/if.c Mon Apr 4 03:43:13 2011 (r220316)
+++ head/sys/net/if.c Mon Apr 4 07:45:08 2011 (r220317)
@@ -465,8 +465,8 @@ if_alloc(u_char type)
}
/*
- * Do the actual work of freeing a struct ifnet, associated index, and layer
- * 2 common structure. This call is made when the last reference to an
+ * Do the actual work of freeing a struct ifnet, and layer 2 common
+ * structure. This call is made when the last reference to an
* interface is released.
*/
static void
@@ -476,13 +476,6 @@ if_free_internal(struct ifnet *ifp)
KASSERT((ifp->if_flags & IFF_DYING),
("if_free_internal: interface not dying"));
- IFNET_WLOCK();
- KASSERT(ifp == ifnet_byindex_locked(ifp->if_index),
- ("%s: freeing unallocated ifnet", ifp->if_xname));
-
- ifindex_free_locked(ifp->if_index);
- IFNET_WUNLOCK();
-
if (if_com_free[ifp->if_alloctype] != NULL)
if_com_free[ifp->if_alloctype](ifp->if_l2com,
ifp->if_alloctype);
@@ -513,6 +506,14 @@ if_free_type(struct ifnet *ifp, u_char t
ifp->if_alloctype));
ifp->if_flags |= IFF_DYING; /* XXX: Locking */
+
+ IFNET_WLOCK();
+ KASSERT(ifp == ifnet_byindex_locked(ifp->if_index),
+ ("%s: freeing unallocated ifnet", ifp->if_xname));
+
+ ifindex_free_locked(ifp->if_index);
+ IFNET_WUNLOCK();
+
if (!refcount_release(&ifp->if_refcount))
return;
if_free_internal(ifp);
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